Does the Emergency Doctrine Need to be Pled as an Affirmative Defense?

Seems like a basic question: Does the "emergency doctrine" need to be pled as an affirmative defense?  Well here's a typical answer: "It depends."

The Appellate Division, First Department recently addressed this threshold issue in Edwards v. New York City Tr. Auth.  The emergency doctrine stands for the proposition that when an actor is faced with a sudden and unexpected circumstance which leaves little or no time for thought, deliberation or consideration, the actor may not be found negligent if the actions are "reasonably prudent" under the emergency circumstances with which he or she is confronted.

Frequently, defendants forget to plead the doctrine as an affirmative defense.  Is this omission fatal? The Edwards Majority and Dissent both conclude that the omission is not fatal where there is evidence that such a defense will not pose a surprise to the plaintiff or co-defendant.  The Majority and Dissent disagreed as to whether an issue of fact existed as to whether the bus driver in this case was actually confronted with an emergency situation.